The present invention relates to a soft (non-metal) sealing material, more particularly to compositions for a soft (non-metal) sealing material, to a process for the preparation thereof, to a novel soft (non-metal) sealing material made according to said process in planar form such as plates, continuous bands, and to the use thereof for technical and industrial applications such as gaskets for flanges, valves, pumps, heat exchangers and pressure vessels, for use in the construction of power plants, chemical plants and heating systems, where it is necessary to provide for an optimum balance between the sealability of the sealing assembly and the thermal as well as chemical resistance of the sealing material employed.
It was tried to develop and to produce, in an economical manner, a sealing material by an environmentally friendly paper process or paper and calender manufacturing process, which material would not contain substances detrimental to health and would show appropriate functional properties when used at higher temperatures and, besides, it would not emit substances detrimental to health above the permissible limit into the environment.
With increasing health and environment consciousness, in products on the basis of elastomers vulcanization agents have recently started to be used which do not cause the formation of cancerogenic N-nitrosamines. Thus, in DE 4038946 the use of said vulcanization agents for the manufacture of rubber sealing rings is disclosed and in EP 0915133 the use thereof for the manufacture of rubber articles for use in medicine is disclosed. In the manufacture of soft sealing materials made from a mixture of different kinds of fibers, binders and fillers, among them being also graphite (U.S. Pat. Nos. 5,437,920; 4,529,653), various additives are mentioned, yet the use of vulcanization agents that do not form dangerous N-nitrosamines above the permissible limit is not disclosed. In U.S. Pat. No. 5,437,920 a sealing material is disclosed, wherein by using 0.5 to 1.5% of non-fibrillated organic staple fibers having an elongation at break up to 200xc2x0 C. under 2% in combination with 2 to 4% of fibrillated polyaramide fibers and at least 60% of powdered graphite good thermal properties (small changes in thickness at compression loading of the material at elevated temperatures) of the sealing material are achieved, whereas the material without the use of non-fibrillated fibers shows greater changes in thickness under the same conditions. In this patent specification no special ecological advantages are mentioned except that no asbestos is contained therein and that it is produced by paper process or paper and calender process without the use of organic solvents.